tomcat源码--springboot整合tomcat源码分析

1.测试代码，一个简单的springboot web项目：地址：https://gitee.com/yangxioahui/demo_mybatis.git

一：tomcat的主要架构：1.如果我们下载了tomcat的安装包，可以在解压后的文件夹看到server.xml文件：

 内容如下：

<?xml version='1.0' encoding='utf-8'?>

<Server port="8005" shutdown="SHUTDOWN">
  <Listener className="org.apache.catalina.startup.VersionLoggerListener" />
  <Listener className="org.apache.catalina.core.AprLifecycleListener" SSLEngine="on" />
  <!--Initialize Jasper prior to webapps are loaded. Documentation at /docs/jasper-howto.html -->
  <Listener className="org.apache.catalina.core.JasperListener" />
  <!-- Prevent memory leaks due to use of particular java/javax APIs-->
  <Listener className="org.apache.catalina.core.JreMemoryLeakPreventionListener" />
  <Listener className="org.apache.catalina.mbeans.GlobalResourcesLifecycleListener" />
  <Listener className="org.apache.catalina.core.ThreadLocalLeakPreventionListener" />
  <GlobalNamingResources>
    <Resource name="UserDatabase" auth="Container"
              type="org.apache.catalina.UserDatabase"
              description="User database that can be updated and saved"
              factory="org.apache.catalina.users.MemoryUserDatabaseFactory"
              pathname="conf/tomcat-users.xml" />
  </GlobalNamingResources>
  <Service name="Catalina">
    <Connector port="8080" protocol="HTTP/1.1"
               connectionTimeout="20000"
               redirectPort="8443" />

    <Connector port="8009" protocol="AJP/1.3" redirectPort="8443" />

    <Engine name="Catalina" defaultHost="localhost">

      <Realm className="org.apache.catalina.realm.LockOutRealm">
        <Realm className="org.apache.catalina.realm.UserDatabaseRealm"
               resourceName="UserDatabase"/>
      </Realm>

      <Host name="localhost"  appBase="webapps"
            unpackWARs="true" autoDeploy="true">

        <Valve className="org.apache.catalina.valves.AccessLogValve" directory="logs"
               prefix="localhost_access_log." suffix=".txt"
               pattern="%h %l %u %t &quot;%r&quot; %s %b" />
        <Context path="/shop" docBase="D:shopdemoweb" debug="0" reloadable="true"> 

      </Host>
    </Engine>
  </Service>
</Server>

从server.xml中我们可以分析出如下关系：

 上图wrapper是我根据tomcat源码补上去的，在server.xml中并没有体现出来，通过上图，大概分析下他们的关系，记得不要在意每个节点的意思：

 由于在java中一切皆对象，所以结合上图我们分析：

    一个tomcat对象中会包含一个server对象，一个server对象可以包含多个service对象，一个service对象，可以包含多个connector对象（用于接收TCP连接）和一个Engine对象；

   一个Engine可以包含多个Host对象，而每个Host可以包含多个context(我们写的每个项目就是一个context),每个Context会包含多个Wrapper对象，而每个Wrapper都会包含一个servlet；

从Engine节点往下包含它自己，都称为容器Container

 伪代码实现如下：

　　Tomcat tomcat=new Tomcat();

　　Server server=new Server();

　　tomcat.setServer(server);

　　Service service=new Service();

　　server.addService(service); //存到集合中

　　Connector connector=new Connector();

　　service.setConnector(connector);

　　Engine engine=new Engine();

　　service.setEngine(engine);

       ..... 省略

 
在tomcat中，命名上面的节点都喜欢使用StandardXX，如StandardServer，StandardService；

 

 

 

 

 

 

 通过这些节点的类，我们发现Engine节点和其包含的子节点都是继承了ContainerBase这个类，所以为何说Engine这个节点和其子节点都叫做容器的道理了：

我们仔细查看上面的节点类，发现他们都继承了生命周期相关的类：LifecycleMBeanBase：

 所以他们都会有对应的生命周期相关方法，这些节点通过生命周期的方法进行串联起来，如tomcat.start()->server.start()->servece.start()->engine.start().........

 二.springboot内嵌tomcat源码分析：

有了上面的基础，我们分析springboot内嵌tomcat的源码就比较方便了： 启动项目，debug调试，可以跟踪到内嵌tomcat的源码：

 //下面从createWebServer() 开始就是我们要分析的源码了，它在ServletWebServerApplicationContext这个类中

private void createWebServer() {
        WebServer webServer = this.webServer; //第一次过来，这个为null
        ServletContext servletContext = getServletContext(); //这个也是null
        if (webServer == null && servletContext == null) {
            ServletWebServerFactory factory = getWebServerFactory();//获取tomcat工厂
            this.webServer = factory.getWebServer(getSelfInitializer());//通过工厂类获取服务器对象。这个是核心
            getBeanFactory().registerSingleton("webServerGracefulShutdown",
                    new WebServerGracefulShutdownLifecycle(this.webServer));
            getBeanFactory().registerSingleton("webServerStartStop",
                    new WebServerStartStopLifecycle(this, this.webServer));
        }
        else if (servletContext != null) {
            try {
                getSelfInitializer().onStartup(servletContext);
            }
            catch (ServletException ex) {
                throw new ApplicationContextException("Cannot initialize servlet context", ex);
            }
        }
        initPropertySources();
    }

上面代码主要是通过web工厂，创建webserver对象，那web工厂有哪些呢？

 这里我们用的是tomcat,所以webserver工厂就自然是TomcatServletWebServerFactory，之后就看它是如何创建tomcat的

 

    @Override
    public WebServer getWebServer(ServletContextInitializer... initializers) {
        if (this.disableMBeanRegistry) {
            Registry.disableRegistry();
        }
        Tomcat tomcat = new Tomcat(); //创建tomcat对象了
        File baseDir = (this.baseDirectory != null) ? this.baseDirectory : createTempDir("tomcat");
        tomcat.setBaseDir(baseDir.getAbsolutePath());
        Connector connector = new Connector(this.protocol); //创建connector了，根据之前tomcat架构分析，这里的connector最终会包含在service里
        connector.setThrowOnFailure(true);
        tomcat.getService().addConnector(connector); //这里获取service,获取不到，就会创建，然后设置到Connector到service中
        customizeConnector(connector);
        tomcat.setConnector(connector);
        tomcat.getHost().setAutoDeploy(false);//获取Host节点，获取不到就会创建Host
        configureEngine(tomcat.getEngine());//创建Engine,在里面会将Host设置到Engine里面
        for (Connector additionalConnector : this.additionalTomcatConnectors) {
            tomcat.getService().addConnector(additionalConnector);
        }
        prepareContext(tomcat.getHost(), initializers);//创建Connext，在里面会将Context设置到host里面
        return getTomcatWebServer(tomcat);//启动各个组件的生命周期的方法
    }

 上面的方法，主要是创建tomcat的架构的各种主件，并且将它们的关系串联起来，之后就调用组件的生命周期方法：

分析几个重要的方法，在tomcat中，通过tomcat.getXX主件，获取不到，内部会创建1. tomcat.getService().addConnector(connector); //由于创建service之前需要创建server，因为server节点是包含service的：

public Service getService() {
        return getServer().findServices()[0];
 }
public Server getServer() {

        if (server != null) {
            return server;
        }

        System.setProperty("catalina.useNaming", "false");

        server = new StandardServer(); //创建server节点了

        initBaseDir();

        // Set configuration source
        ConfigFileLoader.setSource(new CatalinaBaseConfigurationSource(new File(basedir), null));

        server.setPort( -1 );

        Service service = new StandardService(); //创建service节点了
        service.setName("Tomcat");
        server.addService(service); //将service节点加到server节点中
        return server;
    }

  2.tomcat.getHost().setAutoDeploy(false); //根据tomcat架构分析，创建Host前一定会创建Engine

 3.prepareContext(tomcat.getHost(), initializers); 这里开始创建Context节点了，并将其加到Host中

protected void prepareContext(Host host, ServletContextInitializer[] initializers) {
        File documentRoot = getValidDocumentRoot();
        TomcatEmbeddedContext context = new TomcatEmbeddedContext();//继承于StandardContext
        if (documentRoot != null) {
            context.setResources(new LoaderHidingResourceRoot(context));
        }
        context.setName(getContextPath());
        context.setDisplayName(getDisplayName());
        context.setPath(getContextPath());
        File docBase = (documentRoot != null) ? documentRoot : createTempDir("tomcat-docbase");
        context.setDocBase(docBase.getAbsolutePath());
        context.addLifecycleListener(new FixContextListener());
        context.setParentClassLoader((this.resourceLoader != null) ? this.resourceLoader.getClassLoader()
                : ClassUtils.getDefaultClassLoader());
        resetDefaultLocaleMapping(context);
        addLocaleMappings(context);
        try {
            context.setCreateUploadTargets(true);
        }
        catch (NoSuchMethodError ex) {
            // Tomcat is < 8.5.39. Continue.
        }
        configureTldSkipPatterns(context);
        WebappLoader loader = new WebappLoader();
        loader.setLoaderClass(TomcatEmbeddedWebappClassLoader.class.getName());
        loader.setDelegate(true);
        context.setLoader(loader);
        if (isRegisterDefaultServlet()) {
            addDefaultServlet(context); //context中添加servelet,这里添加的并不是我们业务代码创建的servlet，而是默认的
        }
        if (shouldRegisterJspServlet()) {
            addJspServlet(context); //
            addJasperInitializer(context);
        }
        context.addLifecycleListener(new StaticResourceConfigurer(context));
        ServletContextInitializer[] initializersToUse = mergeInitializers(initializers);
        host.addChild(context); //将Context添加到Host节点
        configureContext(context, initializersToUse);
        postProcessContext(context);
    }

4.我们看看servlet如何添加到Context中的

至此，tomcat架构的主要主件已经被串起来了，接下来要分析的是主件的生命周期启动过程：

protected TomcatWebServer getTomcatWebServer(Tomcat tomcat) {
   return new TomcatWebServer(tomcat, getPort() >= 0, getShutdown());
}
public TomcatWebServer(Tomcat tomcat, boolean autoStart, Shutdown shutdown) {
        Assert.notNull(tomcat, "Tomcat Server must not be null");
        this.tomcat = tomcat;
        this.autoStart = autoStart;
        this.gracefulShutdown = (shutdown == Shutdown.GRACEFUL) ? new GracefulShutdown(tomcat) : null;
        initialize(); //开始初始化
    }

    private void initialize() throws WebServerException {
        logger.info("Tomcat initialized with port(s): " + getPortsDescription(false));
        synchronized (this.monitor) {
            try {
                addInstanceIdToEngineName();

                Context context = findContext();
                context.addLifecycleListener((event) -> {
                    if (context.equals(event.getSource()) && Lifecycle.START_EVENT.equals(event.getType())) {
                        // Remove service connectors so that protocol binding doesn't
                        // happen when the service is started.
                        removeServiceConnectors();
                    }
                });

                // Start the server to trigger initialization listeners
                this.tomcat.start(); //开始启动主件的生命周期方法

                // We can re-throw failure exception directly in the main thread
                rethrowDeferredStartupExceptions();

                try {
                    ContextBindings.bindClassLoader(context, context.getNamingToken(), getClass().getClassLoader());
                }
                catch (NamingException ex) {
                    // Naming is not enabled. Continue
                }

                // Unlike Jetty, all Tomcat threads are daemon threads. We create a
                // blocking non-daemon to stop immediate shutdown
                startDaemonAwaitThread();
            }
            catch (Exception ex) {
                stopSilently();
                destroySilently();
                throw new WebServerException("Unable to start embedded Tomcat", ex);
            }
        }
    }

从这里开始this.tomcat.start();将会是我们要重点关注的逻辑了：

我们知道tomcat架构第一个主件是server，所以肯定接下来是server.start()

 我们继续跟进，server.start(); //这里开始要注意了，主件的start()方法是在父类LifecycleBase 中的，因此，后续的主件调用也是调用父类的start方法

 @Override
    public final synchronized void start() throws LifecycleException {

        if (LifecycleState.STARTING_PREP.equals(state) || LifecycleState.STARTING.equals(state) ||
                LifecycleState.STARTED.equals(state)) {

            if (log.isDebugEnabled()) {
                Exception e = new LifecycleException();
                log.debug(sm.getString("lifecycleBase.alreadyStarted", toString()), e);
            } else if (log.isInfoEnabled()) {
                log.info(sm.getString("lifecycleBase.alreadyStarted", toString()));
            }

            return;
        }

        if (state.equals(LifecycleState.NEW)) {
            init();   //第一次进来先调用初始化，运用多态的思想，具体逻辑由子类实现
        } else if (state.equals(LifecycleState.FAILED)) {
            stop();
        } else if (!state.equals(LifecycleState.INITIALIZED) &&
                !state.equals(LifecycleState.STOPPED)) {
            invalidTransition(Lifecycle.BEFORE_START_EVENT);
        }

        try {
            setStateInternal(LifecycleState.STARTING_PREP, null, false);
            startInternal();  //初始化完，开始调用内部的start方法
            if (state.equals(LifecycleState.FAILED)) {
                // This is a 'controlled' failure. The component put itself into the
                // FAILED state so call stop() to complete the clean-up.
                stop();
            } else if (!state.equals(LifecycleState.STARTING)) {
                // Shouldn't be necessary but acts as a check that sub-classes are
                // doing what they are supposed to.
                invalidTransition(Lifecycle.AFTER_START_EVENT);
            } else {
                setStateInternal(LifecycleState.STARTED, null, false);
            }
        } catch (Throwable t) {
            // This is an 'uncontrolled' failure so put the component into the
            // FAILED state and throw an exception.
            handleSubClassException(t, "lifecycleBase.startFail", toString());
        }
    }

从上面方法可知，所有主件都会先调用int()-> startInternal();

我们继续跟进startInternal();

service.start(); 最终也是调用父类的对应方法，跟进去看看

    我们只要看startInternal();方法即可

 protected void startInternal() throws LifecycleException {

        if(log.isInfoEnabled())
            log.info(sm.getString("standardService.start.name", this.name));
        setState(LifecycleState.STARTING);

        // Start our defined Container first
        if (engine != null) {
            synchronized (engine) {
                engine.start(); //这里启动engine->启动host->context
            }
        }

        synchronized (executors) {
            for (Executor executor: executors) {
                executor.start();
            }
        }
        //----- 走到下面的代码说明上面的容器节点都执行完生命周期了------------------
        mapperListener.start(); //启动监听器，这个是重点，因为servlet交给tomcat是在这里做的

        // Start our defined Connectors second
        synchronized (connectorsLock) {
            for (Connector connector: connectors) {
                // If it has already failed, don't try and start it
                if (connector.getState() != LifecycleState.FAILED) {
                    connector.start(); //启动连接器，这里也是重点，这个是初始化NIO的服务端，开始监听客户端请求
                }
            }
        }
    }

通过上面的service的start()方法，我们发现其会调用容器的start方法，之后调用mapperListener的start方法，最后调用Connector的start()方法，开始监听服务。我们一个个看：

1.engine.start()，之后也是调用父类的方法，所以只要看startInternal(); 从这里开始都是容器的启动，实现

 @Override
    protected synchronized void startInternal() throws LifecycleException {

        // Start our subordinate components, if any
        logger = null;
        getLogger();
        Cluster cluster = getClusterInternal();
        if (cluster instanceof Lifecycle) {
            ((Lifecycle) cluster).start();
        }
        Realm realm = getRealmInternal();
        if (realm instanceof Lifecycle) {
            ((Lifecycle) realm).start();
        }

        // Start our child containers, if any
        Container children[] = findChildren(); //获取子容器，这里的子容器
        List<Future<Void>> results = new ArrayList<>();
        for (Container child : children) {
            results.add(startStopExecutor.submit(new StartChild(child))); //使用线程池启动子容器StartChild实现了Callable接口
        }

        MultiThrowable multiThrowable = null;

        for (Future<Void> result : results) {
            try {
                result.get();
            } catch (Throwable e) {
                log.error(sm.getString("containerBase.threadedStartFailed"), e);
                if (multiThrowable == null) {
                    multiThrowable = new MultiThrowable();
                }
                multiThrowable.add(e);
            }

        }
        if (multiThrowable != null) {
            throw new LifecycleException(sm.getString("containerBase.threadedStartFailed"),
                    multiThrowable.getThrowable());
        }

        // Start the Valves in our pipeline (including the basic), if any
        if (pipeline instanceof Lifecycle) {
            ((Lifecycle) pipeline).start();
        }

        setState(LifecycleState.STARTING);

        // Start our thread
        if (backgroundProcessorDelay > 0) {
            monitorFuture = Container.getService(ContainerBase.this).getServer()
                    .getUtilityExecutor().scheduleWithFixedDelay(
                            new ContainerBackgroundProcessorMonitor(), 0, 60, TimeUnit.SECONDS);
        }
    }

startStopExecutor.submit(new StartChild(child))；//容器的启动会调用该方法

Host的启动，会调用Context的启动，逻辑跟前面一样

 

 Context的启动会调用Wrapper的启动

 之后的Wrapper的start()；后续就不分析了，现在小结生命周期的流程：

 1.问题：tomcat接收到Http请求后，如何通过url找到对应的servlet的？

    回答上述问题，先看看service的生命周期调用中，调用了mapperListener.start();我们看看它做了啥？ 因为mapperListener也是实现生命周期接口的，所以我们看其：

   startInternal();方法：

 

 @Override
    public void startInternal() throws LifecycleException {

        setState(LifecycleState.STARTING);

        Engine engine = service.getContainer();
        if (engine == null) {
            return;
        }

        findDefaultHost();

        addListeners(engine);

        Container[] conHosts = engine.findChildren();
        for (Container conHost : conHosts) {
            Host host = (Host) conHost;
            if (!LifecycleState.NEW.equals(host.getState())) {
                // Registering the host will register the context and wrappers
                registerHost(host); //根进这个方法
            }
        }
    }

private void registerHost(Host host) {

        String[] aliases = host.findAliases();
        mapper.addHost(host.getName(), aliases, host);

        for (Container container : host.findChildren()) {
            if (container.getState().isAvailable()) {
                registerContext((Context) container); //跟进这里，因为Context包含了wrapper,而Wrapper包含了Servlet,servlet是有对应的映射路径的
            }
        }

        // Default host may have changed
        findDefaultHost();

        if(log.isDebugEnabled()) {
            log.debug(sm.getString("mapperListener.registerHost",
                    host.getName(), domain, service));
        }
    }

 private void registerContext(Context context) {

        String contextPath = context.getPath();
        if ("/".equals(contextPath)) {
            contextPath = "";
        }
        Host host = (Host)context.getParent();

        WebResourceRoot resources = context.getResources();
        String[] welcomeFiles = context.findWelcomeFiles();
        List<WrapperMappingInfo> wrappers = new ArrayList<>();

        for (Container container : context.findChildren()) {
            prepareWrapperMappingInfo(context, (Wrapper) container, wrappers); //将wrapper封装成WrapperMappingInfo
       
        }

        mapper.addContextVersion(host.getName(), host, contextPath,
                context.getWebappVersion(), context, welcomeFiles, resources,
                wrappers); //加到Mapper对象中

    }

 通过上图可知，经过prepareWrapperMappingInfo（）方法，将Context容器中的所有Wrapper都封装成了WrapperMappingInfo对象了：

之后我们根据mapper.addContextVersion（） 方法： 省略部分代码后：下面的代码存在Mapper这个类中

 protected void addWrapper(ContextVersion context, String path,
            Wrapper wrapper, boolean jspWildCard, boolean resourceOnly) {

        synchronized (context) {
            if (path.endsWith("/*")) {
                // Wildcard wrapper //如果匹配的路径是通配符
                String name = path.substring(0, path.length() - 2);
                MappedWrapper newWrapper = new MappedWrapper(name, wrapper,
                        jspWildCard, resourceOnly);
                MappedWrapper[] oldWrappers = context.wildcardWrappers;
                MappedWrapper[] newWrappers = new MappedWrapper[oldWrappers.length + 1];
                if (insertMap(oldWrappers, newWrappers, newWrapper)) {
                    context.wildcardWrappers = newWrappers; //加到ContextVersion 的WildcardWrapper数组中
                    int slashCount = slashCount(newWrapper.name);
                    if (slashCount > context.nesting) {
                        context.nesting = slashCount;
                    }
                }
            } else if (path.startsWith("*.")) {
                // Extension wrapper  //如果是拓展名结尾的映射路径
                String name = path.substring(2);
                MappedWrapper newWrapper = new MappedWrapper(name, wrapper,
                        jspWildCard, resourceOnly);
                MappedWrapper[] oldWrappers = context.extensionWrappers;
                MappedWrapper[] newWrappers =
                    new MappedWrapper[oldWrappers.length + 1];
                if (insertMap(oldWrappers, newWrappers, newWrapper)) {
                    context.extensionWrappers = newWrappers; //加到ContextVersion 的extensionWrappers数组中
                }
            } else if (path.equals("/")) {
                // Default wrapper
                MappedWrapper newWrapper = new MappedWrapper("", wrapper,
                        jspWildCard, resourceOnly);
                context.defaultWrapper = newWrapper; //默认的，我们这个的是默认的
            } else {
                // Exact wrapper
                final String name;
                if (path.length() == 0) {
                    // Special case for the Context Root mapping which is
                    // treated as an exact match
                    name = "/";
                } else {
                    name = path;
                }
                MappedWrapper newWrapper = new MappedWrapper(name, wrapper,
                        jspWildCard, resourceOnly);
                MappedWrapper[] oldWrappers = context.exactWrappers;
                MappedWrapper[] newWrappers = new MappedWrapper[oldWrappers.length + 1];
                if (insertMap(oldWrappers, newWrappers, newWrapper)) {
                    context.exactWrappers = newWrappers; //ContextVersion 的精确匹配的exactWrappers 数组中
                }
            }
        }
    }

通过上面的分析，我们可以清晰的看到，Servlet的路径不一样，最后存到ContextVersion中的数组也是不一样，分为：通配符匹配，拓展名匹配，默认匹配，精确匹配，我们看看ContextVersion对象：

 我们已经知道Mapper的内部类存有所有的servlet包装类，并且也根据不同的路径分类了，那接下来，我们分析下请求过来时，如何查找对应的servlet: 还是在Mapper这个类

private final void internalMapWrapper(ContextVersion contextVersion,
                                          CharChunk path,
                                          MappingData mappingData) throws IOException {

        int pathOffset = path.getOffset();
        int pathEnd = path.getEnd();
        boolean noServletPath = false;

        int length = contextVersion.path.length();
        if (length == (pathEnd - pathOffset)) {
            noServletPath = true;
        }
        int servletPath = pathOffset + length;
        path.setOffset(servletPath);

        // Rule 1 -- Exact Match  //精确匹配 匹配到的wrapper会存到mappingData
        MappedWrapper[] exactWrappers = contextVersion.exactWrappers;
        internalMapExactWrapper(exactWrappers, path, mappingData);

        // Rule 2 -- Prefix Match //通配符匹配 匹配到的wrapper会存到mappingData
        boolean checkJspWelcomeFiles = false;
        MappedWrapper[] wildcardWrappers = contextVersion.wildcardWrappers;
        if (mappingData.wrapper == null) {
            internalMapWildcardWrapper(wildcardWrappers, contextVersion.nesting,
                                       path, mappingData);
            if (mappingData.wrapper != null && mappingData.jspWildCard) {
                char[] buf = path.getBuffer();
                if (buf[pathEnd - 1] == '/') {
                    /*
                     * Path ending in '/' was mapped to JSP servlet based on
                     * wildcard match (e.g., as specified in url-pattern of a
                     * jsp-property-group.
                     * Force the context's welcome files, which are interpreted
                     * as JSP files (since they match the url-pattern), to be
                     * considered. See Bugzilla 27664.
                     */
                    mappingData.wrapper = null;
                    checkJspWelcomeFiles = true;
                } else {
                    // See Bugzilla 27704
                    mappingData.wrapperPath.setChars(buf, path.getStart(),
                                                     path.getLength());
                    mappingData.pathInfo.recycle();
                }
            }
        }

        if(mappingData.wrapper == null && noServletPath &&
                contextVersion.object.getMapperContextRootRedirectEnabled()) {
            // The path is empty, redirect to "/"
            path.append('/');
            pathEnd = path.getEnd();
            mappingData.redirectPath.setChars
                (path.getBuffer(), pathOffset, pathEnd - pathOffset);
            path.setEnd(pathEnd - 1);
            return;
        }

        // Rule 3 -- Extension Match //拓展名匹配 匹配到的wrapper会存到mappingData
        MappedWrapper[] extensionWrappers = contextVersion.extensionWrappers;
        if (mappingData.wrapper == null && !checkJspWelcomeFiles) {
            internalMapExtensionWrapper(extensionWrappers, path, mappingData,
                    true);
        }

        // Rule 4 -- Welcome resources processing for servlets //欢迎页匹配
        if (mappingData.wrapper == null) {
            boolean checkWelcomeFiles = checkJspWelcomeFiles;
            if (!checkWelcomeFiles) {
                char[] buf = path.getBuffer();
                checkWelcomeFiles = (buf[pathEnd - 1] == '/');
            }
            if (checkWelcomeFiles) {
                for (int i = 0; (i < contextVersion.welcomeResources.length)
                         && (mappingData.wrapper == null); i++) {
                    path.setOffset(pathOffset);
                    path.setEnd(pathEnd);
                    path.append(contextVersion.welcomeResources[i], 0,
                            contextVersion.welcomeResources[i].length());
                    path.setOffset(servletPath);

                    // Rule 4a -- Welcome resources processing for exact macth
                    internalMapExactWrapper(exactWrappers, path, mappingData);

                    // Rule 4b -- Welcome resources processing for prefix match
                    if (mappingData.wrapper == null) {
                        internalMapWildcardWrapper
                            (wildcardWrappers, contextVersion.nesting,
                             path, mappingData);
                    }

                    // Rule 4c -- Welcome resources processing
                    //            for physical folder
                    if (mappingData.wrapper == null
                        && contextVersion.resources != null) {
                        String pathStr = path.toString();
                        WebResource file =
                                contextVersion.resources.getResource(pathStr);
                        if (file != null && file.isFile()) {
                            internalMapExtensionWrapper(extensionWrappers, path,
                                                        mappingData, true);
                            if (mappingData.wrapper == null
                                && contextVersion.defaultWrapper != null) {
                                mappingData.wrapper =
                                    contextVersion.defaultWrapper.object;
                                mappingData.requestPath.setChars
                                    (path.getBuffer(), path.getStart(),
                                     path.getLength());
                                mappingData.wrapperPath.setChars
                                    (path.getBuffer(), path.getStart(),
                                     path.getLength());
                                mappingData.requestPath.setString(pathStr);
                                mappingData.wrapperPath.setString(pathStr);
                            }
                        }
                    }
                }

                path.setOffset(servletPath);
                path.setEnd(pathEnd);
            }

        }

        /* welcome file processing - take 2
         * Now that we have looked for welcome files with a physical
         * backing, now look for an extension mapping listed
         * but may not have a physical backing to it. This is for
         * the case of index.jsf, index.do, etc.
         * A watered down version of rule 4
         */
        if (mappingData.wrapper == null) {
            boolean checkWelcomeFiles = checkJspWelcomeFiles;
            if (!checkWelcomeFiles) {
                char[] buf = path.getBuffer();
                checkWelcomeFiles = (buf[pathEnd - 1] == '/');
            }
            if (checkWelcomeFiles) {
                for (int i = 0; (i < contextVersion.welcomeResources.length)
                         && (mappingData.wrapper == null); i++) {
                    path.setOffset(pathOffset);
                    path.setEnd(pathEnd);
                    path.append(contextVersion.welcomeResources[i], 0,
                                contextVersion.welcomeResources[i].length());
                    path.setOffset(servletPath);
                    internalMapExtensionWrapper(extensionWrappers, path,
                                                mappingData, false);
                }

                path.setOffset(servletPath);
                path.setEnd(pathEnd);
            }
        }


        // Rule 7 -- Default servlet //默认servlet匹配，“/” 开头的匹配，springmvc的dispatcherServlet就是这种
        if (mappingData.wrapper == null && !checkJspWelcomeFiles) {
            if (contextVersion.defaultWrapper != null) {
                mappingData.wrapper = contextVersion.defaultWrapper.object;
                mappingData.requestPath.setChars
                    (path.getBuffer(), path.getStart(), path.getLength());
                mappingData.wrapperPath.setChars
                    (path.getBuffer(), path.getStart(), path.getLength());
                mappingData.matchType = MappingMatch.DEFAULT;
            }
            // Redirection to a folder
            char[] buf = path.getBuffer();
            if (contextVersion.resources != null && buf[pathEnd -1 ] != '/') {
                String pathStr = path.toString();
                // Note: Check redirect first to save unnecessary getResource()
                //       call. See BZ 62968.
                if (contextVersion.object.getMapperDirectoryRedirectEnabled()) {
                    WebResource file;
                    // Handle context root
                    if (pathStr.length() == 0) {
                        file = contextVersion.resources.getResource("/");
                    } else {
                        file = contextVersion.resources.getResource(pathStr);
                    }
                    if (file != null && file.isDirectory()) {
                        // Note: this mutates the path: do not do any processing
                        // after this (since we set the redirectPath, there
                        // shouldn't be any)
                        path.setOffset(pathOffset);
                        path.append('/');
                        mappingData.redirectPath.setChars
                            (path.getBuffer(), path.getStart(), path.getLength());
                    } else {
                        mappingData.requestPath.setString(pathStr);
                        mappingData.wrapperPath.setString(pathStr);
                    }
                } else {
                    mappingData.requestPath.setString(pathStr);
                    mappingData.wrapperPath.setString(pathStr);
                }
            }
        }

        path.setOffset(pathOffset);
        path.setEnd(pathEnd);
    }

至此，我们分析完了，servlet如何存到tomcat中，同时tomcat如何通过url查询对应的servlet:

最后我们回去看看Connector的启动流程，看看它又干了啥？

 debug发现，并不是在上面图所示进行Connector进行start(),我们打断点到Connector这个类的startInternal()：

 

 

 继承根进：

 public final void start() throws Exception {
        if (bindState == BindState.UNBOUND) {
            bindWithCleanup();
            bindState = BindState.BOUND_ON_START;
        }
        startInternal();
    }
@Override
    public void startInternal() throws Exception {

        if (!running) {
            running = true;
            paused = false;

            if (socketProperties.getProcessorCache() != 0) {
                processorCache = new SynchronizedStack<>(SynchronizedStack.DEFAULT_SIZE,
                        socketProperties.getProcessorCache());
            }
            if (socketProperties.getEventCache() != 0) {
                eventCache = new SynchronizedStack<>(SynchronizedStack.DEFAULT_SIZE,
                        socketProperties.getEventCache());
            }
            if (socketProperties.getBufferPool() != 0) {
                nioChannels = new SynchronizedStack<>(SynchronizedStack.DEFAULT_SIZE,
                        socketProperties.getBufferPool());
            }

            // Create worker collection
            if (getExecutor() == null) {
                createExecutor();
            }

            initializeConnectionLatch();

            // Start poller thread
            poller = new Poller(); // 这里是重点，该类实现了Runnable
            Thread pollerThread = new Thread(poller, getName() + "-ClientPoller");
            pollerThread.setPriority(threadPriority);
            pollerThread.setDaemon(true);
            pollerThread.start(); //通过线程启动poller这个Runnable

            startAcceptorThread(); //这里也是重点
        }
    }

//我们先看看Poller这个类：

先来补充下NIO的几个组件知识：  Selector选择器，会监听注册到该监听器的SocketChannel的各种事件

 我们回到Poller来，先看其构造器，然后看其run()方法：

 public class Poller implements Runnable {

        private Selector selector;
        private final SynchronizedQueue<PollerEvent> events =
                new SynchronizedQueue<>();//栈结构，用于存储selector监听到的事件

        private volatile boolean close = false;
        // Optimize expiration handling
        private long nextExpiration = 0;

        private AtomicLong wakeupCounter = new AtomicLong(0);

        private volatile int keyCount = 0;

        public Poller() throws IOException {
            this.selector = Selector.open(); //创建选择器，NIO的重要主件之一
        }
  //省略了部分代码
  public void run() {
            // Loop until destroy() is called
            while (true) {

                boolean hasEvents = false;

                try {
                    if (!close) {
                        hasEvents = events();//判断是否有注册事件
                        if (wakeupCounter.getAndSet(-1) > 0) {
                            // If we are here, means we have other stuff to do
                            // Do a non blocking select
                            keyCount = selector.selectNow();
                        } else {
                            keyCount = selector.select(selectorTimeout);
                        }
                        wakeupCounter.set(0);
                    }
                    if (close) {
                        events();
                        timeout(0, false);
                        try {
                            selector.close();
                        } catch (IOException ioe) {
                            log.error(sm.getString("endpoint.nio.selectorCloseFail"), ioe);
                        }
                        break;
                    }
                } catch (Throwable x) {
                    ExceptionUtils.handleThrowable(x);
                    log.error(sm.getString("endpoint.nio.selectorLoopError"), x);
                    continue;
                }
                // Either we timed out or we woke up, process events first
                if (keyCount == 0) {
                    hasEvents = (hasEvents | events());
                }

                Iterator<SelectionKey> iterator =
                    keyCount > 0 ? selector.selectedKeys().iterator() : null; //选择器开始监听事件
                // Walk through the collection of ready keys and dispatch
                // any active event.
                while (iterator != null && iterator.hasNext()) {
                    SelectionKey sk = iterator.next();
                    NioSocketWrapper socketWrapper = (NioSocketWrapper) sk.attachment();
                    // Attachment may be null if another thread has called
                    // cancelledKey()
                    if (socketWrapper == null) {
                        iterator.remove();
                    } else {
                        iterator.remove();
                        processKey(sk, socketWrapper);//如果有事件过来就会 这个是重点，服务器接收到客户端连接事件后就会调用该方法处理客户端的连接
                    }
                }

                // Process timeouts
                timeout(keyCount,hasEvents);
            }

            getStopLatch().countDown();
        }

//根据看看events()：下图当envents这个栈有事件时，其会调用events.poll()方法弹出一个事件，如果是注册事件，就会注册到Selector中：

 

 小结：poller实现了Runnable 接口，其run()方法会进行客户端各种连接事件，而其evens这个栈结构用于存储ServerSocketChannel.accept（）接收到的SocketChannel封装成的事件：

那么：到底是谁将客户端的连接压入Poller的events栈的呢？我们回到下面的代码：

 

 这里有个acceptor主件，跟poller一样，它也实现了Runnable:看看其源码：

acceptor = new Acceptor<>(this); //该方法传入了this(AbstractEndpoint),而this是包含了Poller的，所以Acceptor接收的客户端才能交给Poller;
我们分析下其run方法：

 @Override
    public void run() {

        int errorDelay = 0;

        // Loop until we receive a shutdown command
        while (endpoint.isRunning()) {

            // Loop if endpoint is paused
            while (endpoint.isPaused() && endpoint.isRunning()) {
                state = AcceptorState.PAUSED;
                try {
                    Thread.sleep(50);
                } catch (InterruptedException e) {
                    // Ignore
                }
            }

            if (!endpoint.isRunning()) {
                break;
            }
            state = AcceptorState.RUNNING;

            try {
                //if we have reached max connections, wait
                endpoint.countUpOrAwaitConnection();

                // Endpoint might have been paused while waiting for latch
                // If that is the case, don't accept new connections
                if (endpoint.isPaused()) {
                    continue;
                }

                U socket = null;
                try {
                    // Accept the next incoming connection from the server
                    // socket
                    socket = endpoint.serverSocketAccept();
                } catch (Exception ioe) {
                    // We didn't get a socket
                    endpoint.countDownConnection();
                    if (endpoint.isRunning()) {
                        // Introduce delay if necessary
                        errorDelay = handleExceptionWithDelay(errorDelay);
                        // re-throw
                        throw ioe;
                    } else {
                        break;
                    }
                }
                // Successful accept, reset the error delay
                errorDelay = 0;

                // Configure the socket
                if (endpoint.isRunning() && !endpoint.isPaused()) {
                    // setSocketOptions() will hand the socket off to
                    // an appropriate processor if successful
                    if (!endpoint.setSocketOptions(socket)) {
                        endpoint.closeSocket(socket);
                    }
                } else {
                    endpoint.destroySocket(socket);
                }
            } catch (Throwable t) {
                ExceptionUtils.handleThrowable(t);
                String msg = sm.getString("endpoint.accept.fail");
                // APR specific.
                // Could push this down but not sure it is worth the trouble.
                if (t instanceof Error) {
                    Error e = (Error) t;
                    if (e.getError() == 233) {
                        // Not an error on HP-UX so log as a warning
                        // so it can be filtered out on that platform
                        // See bug 50273
                        log.warn(msg, t);
                    } else {
                        log.error(msg, t);
                    }
                } else {
                        log.error(msg, t);
                }
            }
        }
        state = AcceptorState.ENDED;
    }

 @Override
    public void run() {

        int errorDelay = 0;

        // Loop until we receive a shutdown command
        while (endpoint.isRunning()) {

            // Loop if endpoint is paused
            while (endpoint.isPaused() && endpoint.isRunning()) {
                state = AcceptorState.PAUSED;
                try {
                    Thread.sleep(50);
                } catch (InterruptedException e) {
                    // Ignore
                }
            }

            if (!endpoint.isRunning()) {
                break;
            }
            state = AcceptorState.RUNNING;

            try {
                //if we have reached max connections, wait
                endpoint.countUpOrAwaitConnection();

                // Endpoint might have been paused while waiting for latch
                // If that is the case, don't accept new connections
                if (endpoint.isPaused()) {
                    continue;
                }

                U socket = null;
                try {
                    // Accept the next incoming connection from the server
                    // socket
                    socket = endpoint.serverSocketAccept(); //接收客户端的请求，后续会根据，这个方法会一直阻塞，这也就是为何我们启动springweb项目，不会自动关掉的原因了
                } catch (Exception ioe) {
                    // We didn't get a socket
                    endpoint.countDownConnection();
                    if (endpoint.isRunning()) {
                        // Introduce delay if necessary
                        errorDelay = handleExceptionWithDelay(errorDelay);
                        // re-throw
                        throw ioe;
                    } else {
                        break;
                    }
                }
                // Successful accept, reset the error delay
                errorDelay = 0;

                // Configure the socket
                if (endpoint.isRunning() && !endpoint.isPaused()) {
                    // setSocketOptions() will hand the socket off to
                    // an appropriate processor if successful 
                    if (!endpoint.setSocketOptions(socket)) {//如果接收到了客户端请求，那么就会调用该方法
                        endpoint.closeSocket(socket);
                    }
                } else {
                    endpoint.destroySocket(socket);
                }
            } catch (Throwable t) {
                ExceptionUtils.handleThrowable(t);
                String msg = sm.getString("endpoint.accept.fail");
                // APR specific.
                // Could push this down but not sure it is worth the trouble.
                if (t instanceof Error) {
                    Error e = (Error) t;
                    if (e.getError() == 233) {
                        // Not an error on HP-UX so log as a warning
                        // so it can be filtered out on that platform
                        // See bug 50273
                        log.warn(msg, t);
                    } else {
                        log.error(msg, t);
                    }
                } else {
                        log.error(msg, t);
                }
            }
        }
        state = AcceptorState.ENDED;
    }

 我们根进看看： endpoint.setSocketOptions(socket)

  @Override
    protected boolean setSocketOptions(SocketChannel socket) {
        NioSocketWrapper socketWrapper = null;
        try {
            // Allocate channel and wrapper
            NioChannel channel = null;
            if (nioChannels != null) {
                channel = nioChannels.pop();
            }
            if (channel == null) {
                SocketBufferHandler bufhandler = new SocketBufferHandler(
                        socketProperties.getAppReadBufSize(),
                        socketProperties.getAppWriteBufSize(),
                        socketProperties.getDirectBuffer());
                if (isSSLEnabled()) {
                    channel = new SecureNioChannel(bufhandler, selectorPool, this);
                } else {
                    channel = new NioChannel(bufhandler);
                }
            }
            NioSocketWrapper newWrapper = new NioSocketWrapper(channel, this);
            channel.reset(socket, newWrapper);
            connections.put(socket, newWrapper);
            socketWrapper = newWrapper;

            // Set socket properties
            // Disable blocking, polling will be used
            socket.configureBlocking(false);
            socketProperties.setProperties(socket.socket());

            socketWrapper.setReadTimeout(getConnectionTimeout());
            socketWrapper.setWriteTimeout(getConnectionTimeout());
            socketWrapper.setKeepAliveLeft(NioEndpoint.this.getMaxKeepAliveRequests());
            socketWrapper.setSecure(isSSLEnabled());
            poller.register(channel, socketWrapper);//在这里将会将接收到的客户端封装成事件，存到Poller的envens栈中
            return true;
        } catch (Throwable t) {
            ExceptionUtils.handleThrowable(t);
            try {
                log.error(sm.getString("endpoint.socketOptionsError"), t);
            } catch (Throwable tt) {
                ExceptionUtils.handleThrowable(tt);
            }
            if (socketWrapper == null) {
                destroySocket(socket);
            }
        }
        // Tell to close the socket if needed
        return false;
    }

 //小结上面的流程：

 //最后通过调用Controller的方法，看看整个调用链条：

 

前面分析过，Poller的run方法会处理监听到的事件，所以，我们打个断点在该方法里：

 

 根进去：

 public boolean processSocket(SocketWrapperBase<S> socketWrapper,
            SocketEvent event, boolean dispatch) {
        try {
            if (socketWrapper == null) {
                return false;
            }
            SocketProcessorBase<S> sc = null;
            if (processorCache != null) {
                sc = processorCache.pop();
            }
            if (sc == null) {
                sc = createSocketProcessor(socketWrapper, event); //将客户端封装成sc,sc实现了Runnable接口
            } else {
                sc.reset(socketWrapper, event);
            }
            Executor executor = getExecutor();
            if (dispatch && executor != null) {
                executor.execute(sc); //最终交给了一个线程池处理了
            } else {
                sc.run();
            }
        } catch (RejectedExecutionException ree) {
            getLog().warn(sm.getString("endpoint.executor.fail", socketWrapper) , ree);
            return false;
        } catch (Throwable t) {
            ExceptionUtils.handleThrowable(t);
            // This means we got an OOM or similar creating a thread, or that
            // the pool and its queue are full
            getLog().error(sm.getString("endpoint.process.fail"), t);
            return false;
        }
        return true;
    }

 所以接下来看看：SocketProcessorBase的run方法：

@Override
    public final void run() {
        synchronized (socketWrapper) {
            // It is possible that processing may be triggered for read and
            // write at the same time. The sync above makes sure that processing
            // does not occur in parallel. The test below ensures that if the
            // first event to be processed results in the socket being closed,
            // the subsequent events are not processed.
            if (socketWrapper.isClosed()) {
                return;
            }
            doRun();
        }
    }

继续跟踪doRun();

 一直到这里，我们可以看到，最终会调用Mapper的方法去找到对应的Servlet的，前面已经分析过Mapper有个根据url获取Servelet包装类的放法，并将其存到MappingData中，我们跟进去：

 

 

 

 Pipeline最后一个基本都是xxxValue:

  @Override
    public final void invoke(Request request, Response response)
        throws IOException, ServletException {

        // Disallow any direct access to resources under WEB-INF or META-INF
        MessageBytes requestPathMB = request.getRequestPathMB();
        if ((requestPathMB.startsWithIgnoreCase("/META-INF/", 0)) //这些判断就说明了，为何前端不能直接访问WEB-INF的内容了
                || (requestPathMB.equalsIgnoreCase("/META-INF"))
                || (requestPathMB.startsWithIgnoreCase("/WEB-INF/", 0))
                || (requestPathMB.equalsIgnoreCase("/WEB-INF"))) {
            response.sendError(HttpServletResponse.SC_NOT_FOUND);
            return;
        }

        // Select the Wrapper to be used for this Request
        Wrapper wrapper = request.getWrapper();//前面分析过了，Servlet存到了Request中，这里获取出来
        if (wrapper == null || wrapper.isUnavailable()) {
            response.sendError(HttpServletResponse.SC_NOT_FOUND);
            return;
        }

        // Acknowledge the request
        try {
            response.sendAcknowledgement();
        } catch (IOException ioe) {
            container.getLogger().error(sm.getString(
                    "standardContextValve.acknowledgeException"), ioe);
            request.setAttribute(RequestDispatcher.ERROR_EXCEPTION, ioe);
            response.sendError(HttpServletResponse.SC_INTERNAL_SERVER_ERROR);
            return;
        }

        if (request.isAsyncSupported()) {
            request.setAsyncSupported(wrapper.getPipeline().isAsyncSupported());
        }
        wrapper.getPipeline().getFirst().invoke(request, response);//调用Servlet处理请求
    }

 至此分析完毕整个调用流程